Every time an email is sent from confluence it would be a great feature if someone could reply to that email and then Confluence would take the contents of the reply and place it as a comment to the section of change in question.

So we have a page as follow
Title
line 1
line 2
line 3

Someone changes line 2 a note is sent out to watchers with the change. Any reply would add a comment to line 2.

If it was a brand new page that was added and an email was sent out, then the replies would be added to the bottom comment section.